Thermoelectric refrigerator



March 9, 1965 M. R. COLE THERMOELECTRIC REFRIGERATOR 2 Sheets-Sheet 1Filed Oct. 31. 1962 FIG.

FIG. 2

INVENTOR. M ELROSE R. COLE BY 'ROMQ Sm ATTORNEYS M. R. COLETHERMOELECTRIC REFRIGERATOR March 9, 1965 2 Sheets-Sheet 2 Filed Oct 31,1962 MELROSE R. COLE BY M8} SM.

AT TO RN EYS United States Patent C) This invention relates tothermoelectric refrigerators, and more particularly to improvementswhich will reduce Icw the time required to freeze water to ice in suchrefrigerators.

The art of thermoelectric cooling has reached the state whererefrigerators of small capacity, such as for making ice cubes, arecommercially competitive, in that their simplicity of construction andlow maintenance cost outweigh their comparatively high initial cost. Itis understood that thermoelectric cooling elements are improving sorapidly that refrigerators of larger sizes will soon be similarlyavailable. One characteristic of currently available low-volumerefrigerators which can advantageously be improved is the long timerequired to freeze water from room temperature. In practice, it isdesirable to provide at least two trays of ice cubes, holding togetherabout one kilogram of water. It has been found that a practicalrefrigerator will freeze this quantity of water, from about C. startingtemperature, in about six hours. If a'user then removes one tray of icecubes and substitutes an equal quantity (about 500 grams) of water, itwill take about three hours to freeze the water in the fresh tray.

It is the principal object of this invention to provide a thermoelectricrefrigerator in which when one of two or more ice cube trays is removedand replaced with a tray full of water at room temperature, the waterwill be frozen in less time than heretofore, for example, onethird toone-half of the time heretofore required. According to the invention inits broader aspects, this object is achieved by providing in athermoelectric refrigerator a thermal sink or cold source which ismaintained at low temperature substantially at or below the freezingtemperature of water and which exchanges substantially more calories ingoing from room temperature to the said low temperature than thecontents of one ice-cube tray. Preferably, in a two-tray refrigerator,the thermal capacity of the thermal sink is approximately the same asthat of the water contents of both trays between the same temperaturelimits. Such a thermal sink is cooled by the thermoelectric coolingmeans along with the original charge in the ice cube trays, until theentire system is brought to the temperature at which ice cubes areformed. Thereafter, the refrigerator may continue to operate. Removal ofone tray of ice cubes depletes the cold contents by less than half, andatray of water which replaces the ice cubes is cooled by the combinedefforts of the thermal sink, the remaining ice cubes, and thethermoelectric element. By choosing for the thermal sink a liquid, suchas water, which has a high specific heat, the temperature of the newcharge of water is quickly brought near to the freezing point of water,thereby drastically reducing the time required to freeze a new tray ofice cubes. It is accordingly another important object of the inventionto provide a thermoelectric refrigerator having a heat sink ofsubstantially the same thermal capacity as the material to be cooled,over the same temperature range, particularly for use with two or moreice-cube trays.

I have found that a small thermoelectric refrigerator, capableoriginally of freezing a given quantity of ice over a long period oftime (e.g., six hours or more) can be efiiciently operated to freeze itfresh tray of ice cubes 3,172,269 Patented Mar. 9, 1965 in a shortperiod of time when supplied with a thermal sink according to theinvention. That is, by increasing the initial load on the coolingelement, and thereafter using part of the initial load to help cool newcomponents of the useful load, I have provided a small, or low powerrefrigerator which can be operated to provide quick freezing of icecubes or the like with no increase in power consumed.

The foregoing and other objects and features of the invention willbecome more readily apparent from the following description of certainexemplary embodiments. This description refers to the accompanyingdrawings, wherein:

FIG. 1 is a front-sectional view of an embodiment of the invention;

FIG. 2 is a section along line 22 of FIG. 1;

FIG. 3 is an exploded view, partially schematic, of the embodiment ofFIG. 1; and

FIG. 4 is an isometric view of another embodiment of the invention.

Referring to FIGS. 1, 2 and 3, a thermoelectric cooling device 10,having a heat-absorbing surface 11 and a heat radiating surface 12, isthe cooling means for a thermoelectric refrigerator generally designatedby the reference character 20. A generally U-shaped body 15, which maybe made of aluminum, for example, having first and second horizontalarms 16 and 17 and a vertical bight portion 18, is thermally coupled atthe bight portion to the heat-absorbing surface 11 of the cooling device10. As is shown in FIG. 3, the thermoelectric cooling device, which asillustrated is of a known commercial form, is abutted to the bightportion 18 of the body 15 with a thin film of electrical insulatingmaterial 19 between them. For simplicity of illustration, this film isomitted in FIG. 1. The film 19 may be a plastic, such as the plasticavailable under the commercial or trade designation Mylar, approximately0.001 inch thick, coated on both sides with silicon grease. Whensandwiched between the heat-absorbing surface 11 and the bight portion18 of the body 15, this film affords electrical insulation and minimizesjunction thermal drop in the thermoelectric elements. At the same time,this film, being quite thin, has negligible influence upon the heattransfer across it, from the body 15 to the heat absorbing surface 11.The thermoelectric cooling device 10 is attached to the body 15 by meansof bolts (represented by dashed lines'21, 21) through holes 22, 22 inthe bight portion 18 (FIG. 3). These bolts may preferably be made ofstainless steel.

A tank 25, which may be made of aluminum, copper or brass, for example,is thermally bonded at one side to the free end of one arm 16 of thebody 15, and at the bottom to an extension of the other arm 17. Thisarrangement provides good thermal-conductivity between the tank 25 andthe body 15. The two may conveniently be welded together. The top '26 ofthe tank has an opening with an extension 27 through which it may'be'filled with a liquid 28, and a cap 29 to close the opening. Theproperties of the liquid 29 will be described in some detail .below. Icecube trays 31, 32 may rest on the arms 16, 17, respectively, of the body15, which function as shelves for this purpose.

While it is not material to an understanding of the invention, it willbe understood that a cabinet will in'pract ice surround the tank 25 andbody 15, providing a thermally-insulated compartment (not shown) for thetrays 31, 32. Walls for such a cabinet are indicated at 33. Insulation34 may be contained within such walls, outside of them or between pairsof such walls (no-t shown) as is well-known in the art. The walls 33 andinsulation 34 are indicated only in FIG. 1. In any event, it

will be convenient to fit radiator fins 35 to the heat emitting side 12of the thermoelectric cooling device 10, and these fins will be outsidethe cabinet. A fan (not shown) may be employed to aid in removing heatfrom the fins 35. In addition, it will be understood that a suitableelectric circuit, known in the art, will in practice be provided for thethermoelectric cooling device 10.

The liquid 29 in the tank 25 should be capable of releasing asubstantial quantity of heat energy to the heat absorbing sun-face 11through the thermally conductive shelves 16, 17 of the body 15.Conveniently, the shelves may be about A inch thick, to give themflatness and to implement heat flow. Conversely, a correspondingquantity of heat can be absorbed by the liquid 29 (when .cold) fromwater (not shown) in the trays 31, 32 through the shelves 16, 17,respectively, when water at room temperature is present in the trays.

The liquid 29 is preferably a mixture of water and a suitable chemicalwhich will reduce the freezing point of the mixture to approximately -5C., at which point the mixture preferably becomes a heavy crystal-likeslush. This temperature is selected to be below zero (centigrade) sothat heat will readily transfer to the tank 25 from trays of Water onone or both of the shelves 16, '17, thereby constituting the liquid 29,at such a temperature, a cold reservoir or heat sink adequate for thepurposes of the invention, while at the same time it is suthciently warmto assure an optimum temperature differential between the heat absorbingand heat emitting sides 11 and 12, respectively, of the thermoelectriccooling device 10 to maximize its heat pump efficiency. Ethylene glycol(C H O and alcohol are additives which are suitable to provide a mixturehaving an icecrystal, slush, temperature which is about 6 C. A

vmixtureof 22% by volume of ethylene glycol in water is a preferredblend for optimized performance characteristics in accordance with theforegoing criteria, while assuring minimum expansion associated with thefreezing of water. Where the trays 31, 32 have a capacity of 500 cc.each, the tank 25 may be made of aluminum /8 inch thick, and may have avolume of 1300 milliliters, and the liquid 29 may be 1000 cc. of such aliquid mixture. The shelves 16, 17 may be aluminum A inch or inch thick;The thermoelectric cooling device may have a capacity of 15,000 caloriesper hour, as aheat pump. Operation of a refrigerator with thesecharacteristics will be approximately'as follows:

(a) At initial turn-on, the entire system, including .all parts andwater (not shown) in the trays 31, 32, will be at room temperature,assumed to be 20 C.;

(b) Initial heat pumping action will establish a thermal gradient alongthe shelves, from the thermoelectric device 10 to the tank 25;

(c) During initial cooling, because of the thermal gradient along theshelves 16, 17, heat is removed faster fromthe water in the trays 31, 32than from the liquid 29in the tank 25;

(d) Upon reaching C. at the trays (in about 2 to 2 /2 hours), freezingof the water in the trays begins, and

this temperature is maintained at the trays until all of the latent heatof fusion of the water (80 calories per gram, or 80,000 calories) isgiven up to the heat absorbing surface .11; this will take about fiveand one-half hours additional;

; (a).:Dur-ing the freezing of water in the trays, the liquid mixture 29remains at 0 C., which is above its freezing point; thereafter theentireload (ice in the trays and liquid 29) is further cooled to the freezingpoint (about C. or 6 C.) of the liquid 29, which then gives up itslatent heat of fusion, namely, an additional 80,000 calories,approximately;

(1) With both the liquid 29, and the Water in the trays frozen, therefrigerator will continue to pump the temperature of the load down to aminimum temperature within the capacity of the system.

Thus it is seen that, during initial cooling, the system of thisinvention provides that the ice cubes are frozen before the heat sink isfrozen, which is an advantage that assures that the presence of the heatsink will not significantly delay the production of ice cubes, ascompared with prior thermoelectric refrigerators which do not have aheat sink as herein described. When one or both of the ice cube traysare removed, emptied, and refilled with room temperature water, andreplaced in the refrigerator, during the period when the liquid mixture29 is in the ice crystal state, the liquid mixture 29 and thethermoelectric cooling device 10 will both function as heat pumpsrelative to this freshly introduced water load. If the ice cube traysare filled to the top to contain 1000 grams of water, requiring 100calories per gram to convert it from room temperature water to ice, thiscan be accomplished in less than three hours. The liquid mixture 29,having the aforesaid composition, is 1000 cc. of a 60 calorie per grammixture at a temperature of 6 C., or lower, and therefore represents60,000 calories available to absorb heat from a load warmer than 6 C.Assuming no thermal gradient within the system, and 15,000 calories perhour pumping capacity for the thermoelectric cooling device 10, morethan 100,000 calories can be removed from the Water in three hours. Ifthe trays 31, 32 are filled full, to hold 750 grams of water, then only75,000 calcries are required to be removed to freeze the water, and thiscan be done in 1 hour. One tray, so used, can produce new ice cubes inapproximately one-half hour, even if the contents of a frozen tray areignored. Thus, in the present invention, it is clear that increased heatpumping capacity is afforded for a short time, which is sufficient tofreeze ice cubes for practical purposes, and

this is achieved with a system containing a heat pump reservoir and amedium-to-low' capacity thermoelectric heat pump.

FIG. 4 illustrates an alternative embodiment of the invention in which ametal reservoir tank is thermally coupled at one side to the heatabsorbing surface 62 of a thermoelectric heat pump 60, and at the otherside to the edges of two shelves 66 and 67, madeof thermally conductivematerial. All other details are similar to corresponding details'inFIG. 1. While this embodiment does not appear, as does FIG. 1, toprovide that cooling will be effective at the shelves before beingeffective at the reservoir, the fact that water on the shelves 66, 67will freeze before theliquid 2 (not shown) in the reservoir isinherentin the liquids themselves, so that here, too, ice cubes will bemade before the heat sink liquid 29 freezes. As in FIG. 1, the reservoir55, when charged with an appropriate heat-sink liquid at a temperaturebelow 0 C., will cause quick freezing of water which .is subsequentlyplaced in trays on the shelves 66, 67.

The embodiments of the invention which have been illustrated anddescribed herein are but a few illustrations of the invention. Otherembodiments and modifications will occur to those skilled in the art. Noattempt has been made to illustrate all possible. embodiments of theinvention, .but rather only to illustrate its principles and the bestmanner presently known to practice it. Therefore, while certain specificembodiments have been described as illustrative of the invention, suchother forms as would occur to one skilled in this art on a reading ofthe foregoing specification arealso Within .the spirit and scope of theinvention, and it is intended .meanshaving twohorizontal arms spacedapart to pro- 5 vide shelves and a vertical bight portion, said hightportion being thermally coupled to said heat-absorbing surface and saidarms being thermally-coupled to said thermally-conductive part of saidWall means.

2. In a thermoelectric cooling refrigerator, in combination,thermoelectric means having a heat-absorbing surface and a heat-emittingsurface, a liquid reservoir having Wall means at least a part of whichis thermallyconductive, and U-shaped thermally-conductive shelf meanshaving two horizontal arms spaced apart to provide shelves and avertical bight portion, said hight portion and said heat-absorbingsurface being each thermally coupled to a thermally-conductive part ofsaid wall means.

3. In a thermoelectric cooling refrigerator, in combina- .tion,thermoelectric means having a heat-absorbing surface and a heat-emittingsurface, a liquid tank having metal Walls, and a U-shaped 'body ofaluminum having its two arms horizontally-disposed and fastened at theirfree ends to a Wall of said tank in thermally-conductive relationtherewith, the bight portion of said body being thermally-coupled tosaid heat-absorbing surface.

4. In a thermoelectric cooling refrigerator, in comb-ination,thermoelectric means having a heat-absorbing surface and a heat-emittingsurface, a metal tank of rectangular configuration, and a U-shaped metalbody having its arms horizontally disposed one above the other and itslbight portion vertically disposed, the lower arm 'being longer than theupper arm, said tank having its bottom thermally coupled to a sidesurface of the lower arm and one side Wall of the tank thermally bondedto the free end of the upper arm, said b ight portion b ing thermallycoupled to said heat-absorbing surface.

References Cited in the file of this patent UNITED STATES PATENTS2,255,459 Vretman Sept. 9, 1941 2,664,716 Warmon Jan. 5, 1954 2,978,875Lackey Apr. 11, 1961 3,040,539 Gaugler June 26, 1962 3,064,440 WallerNov. 20, 1962

1. IN A THERMOELECTRIC COOLING REFRIGERATOR, IN COMBINATION,THERMOELECTRIC MEANS HAVING A HEAT-ABSORBING SURFACE AND A HEAT-EMITTINGSURFACE, A LIQUID RESERVOIR HAVING WALL MEANS AT LEAST A PART OF WHICHIS THERMALLYCONDUCTIVE, AND U-SHAPED THERMALLY-CONDUCTIVE SHELF MEANSHAVING TWO HORIZONTAL ARMS SPACED APART TO PROVIDE SHELVES AND AVERTICAL BIGHT PORTION, SAID BIGHT PORTION BEING THERMALLY COUPLED TOSAID HEAT-ABSORBING SURFACE AND SAID ARMS BEING THERMALLY-COUPLED TOSAID THERMALLY-CONDUCTIVE PART OF SAID WALL MEANS.